News Release Number: STScI-2004-12

New Clues About the Nature of Dark Energy: Einstein May Have Been Right After All

February 20, 2004: The good news from NASA's Hubble Space Telescope is that Einstein
was right — maybe. A strange form of energy called "dark energy"
is looking a little more like the repulsive force that Einstein
theorized in an attempt to balance the universe against its own
gravity. Even if Einstein turns out to be wrong, the universe's
dark energy probably won't destroy the universe any sooner than
about 30 billion years from now, say Hubble researchers.

Q & A: Understanding the Discovery

1.
What is dark energy?

Dark energy is an unknown form of energy that radiates from
deep space. It behaves in the opposite manner from gravity.
Rather than pulling galaxies together it pushes them apart.

2.
Did anyone predict dark energy?

Dark energy is a complete surprise. However, Albert Einstein
theorized the existence of a repulsive form of gravity in space
that would balance the universe against normal gravity and keep
it from imploding. Einstein called it the cosmological constant.

3.
How does dark energy affect the universe?

Dark energy makes up the bulk of the universe's mass/energy budget.
If dark energy is stable the universe will continue expanding and
accelerating forever. If dark energy is unstable the universe
could ultimately come unglued to the point where stars, planets
and even atoms come apart, a doomsday scenario called the "big rip."
Dark energy might also flip such that is becomes an attractive
force and causes the universe to implode in a "big crunch."

4.
How can Hubble "see" dark energy?

Hubble can measure the faint glow of distant supernovae, stars that
exploded billions of years ago. Supernovae trace the expansion
history of the universe, hence, how dark energy "pushed" on space
over the past epochs. Every second a star explodes somewhere in the
universe, so it's a matter of Hubble looking in the right place at
the right time.

5.
Does Hubble prove how dark energy really behaves?

These latest Hubble observations show that dark energy is not changing
its behavior over time, and so may be the "constant" Einstein predicted.
However, more observations are needed over the coming decade.

6.
What happens to this research after Hubble stops working?

There will be a hiatus of at least several years in this type of research
until some future space telescope with a wide field of view picks up where
Hubble left off. This type of research cannot be done with even the largest
ground-based telescopes, even those outfitted with adaptive optics for
improving image quality.